In the present disclosure and drawings, the invention and prior art will be described in relation to screws, however it will be understood that any threaded fastener may be used to equal advantage, such as a bolt, or conventional fasteners with a composite shank design having a drill bit tip, thread tapping intermediate shank, and threaded upper shank.
Many screw strips are known whereby the threaded fasteners are connected to each other by a retaining belt, preferably of plastic material, although any frangible material can be used. The strips are engaged by a power-driven screw bit and then screwed into a workpiece. In the course of the bit engaging the screw and driving the screw into the workpiece, the screw breaks away and becomes detached from the plastic strip.
Conventional screw strips and machinery to utilize such strips are described in the prior art U.S. Pat. Nos. 4,167,229 to Keusch et al and 4,146,071 to Meuller et al, the disclosures of which are incorporated by reference herein.
In certain fastening applications there is a need to apply fasteners which include washers. For example, metal cladding panels are attached to the roofs or walls of buildings with self tapping screw fasteners that include a metal washer having a neoprene underside layer to effectively seal the hole made for the fastener in the cladding panel.
One such screw strip which includes washers is disclosed in the applicant's U.S. Pat. No. 4,930,630 to Habermehl issued Jun. 9, 1990. The disclosure in that patent is specifically incorporated by reference herein.
In many applications relatively large sized washers or screw heads are required. Conventional prior art screw strips, if adapted for use with washers, require the spacing between screw fasteners to be extended in order to provide sufficient clearance for such large size washers and screw heads. This type of modification is generally unacceptable since the mechanisms used to index the screw strips in an incremental fashion have a standard maximum fixed incremental distance at which they operate. The indexing mechanisms are typically limited in that the spacing between screw fasteners is not capable of alteration.
It is desirable to maintain the spacing between fasteners at a constant dimension regardless of the size of the washers or the screw heads.
In certain applications a hexagonal head or other externally driven screw head types are desired. Prior art screw strips and devices for driving the screws are of limited application since hexagonal screw heads require a socket driver which envelops the entire screw head. The socket driver itself is of large outer diameter such that the socket driver interferes with the heads or washers of rearwardly adjacent screws in the strip. Damage may result to the socket driver or screw. In order to avoid interference, the spacing between screws on conventional strips must be extended.
The use of socket drivers for hexagonal screw heads and relatively large sized washers virtually eliminates the possibility of using prior screw strips or driving devices. In order to accommodate the large diameter washers and socket drivers, the prior art devices would require that the spacing between connectors be increased. It is highly desirable that the spacing between connectors be standardized at a uniform dimension, such that the relatively expensive indexing mechanisms can be used in association with the wide variety of screw types and sizes.
The use of relatively large sized washers and socket drivers would result in interference between washers and socket drivers unless the spacing between fasteners was increased in prior art devices. Varying the spacing of screws in a strip would require modification or adjustment of the driving mechanism adding to the costs and labour involved.
Therefore it is desirable to have a screw strip and indexing device which accommodates relatively large sized washers and screw heads while maintaining the uniformity of fastener spacing on the strip.
It is also desirable to produce screw strips with washers in as compact a strip as possible to minimize cost of the strip and reduce size for handling.